Technical Field
The present disclosure relates to a combination of a field effect transistor and a bipolar transistor.
Description of the Related Technology
There is often a need to be able to switch relatively high voltages, typically up to and in the 200 Volt to 300 Volt range. Transistors to achieve this may be integrated into an integrated circuit package with lower voltage processing and control circuits. In many instances it is convenient and cost effective for such high voltage transistors to be on the same wafer as the lower voltage control circuits. As a result it can be highly desirable for all of the connections to such a high voltage transistor to be made on the same side of the wafer. Applications for switches in this voltage range include motor control and inverters, light dimmers, automotive switches where transient voltages due to inductive loads may potentially occur and a whole host of mains voltage related switching in industrial and domestic appliances and power supplies for such appliances.
Switching can often be done by high power metal oxide semiconductor field effect transistors (MOSFETS) and the like. However it is often desirable for the drive loading presented by such a transistor to be as small as possible, and this tends to be a problem with relatively large MOSFETS as although they take no substantial gate current under conditions when the gate is being held at a constant voltage, the gate has a relatively large capacitance and hence current flows to and from the gate during transistor switching may result in large transient current flows that may perturb the operation of other circuits or induce noise in them by virtue of supply rail voltage fluctuations that such large current flows can induce.
Other considerations also become a factor when choosing a switching technology. The high voltage MOSFETs (e.g., double-diffused metal oxide semiconductor (DMOS) transistors) generally have a competitive advantage over insulated gate bipolar transistors (IGBT) in the lower voltage switching ranges, with IGBTs becoming favoured as the voltage increases past 700 V to 800 V or so.